Definition
Perihelion (from Greek peri, near, and helios, Sun) is the orbital point nearest the Sun. The opposite point is aphelion. For an elliptical orbit, the heliocentric distance at perihelion is a(1 − e), where a is the semi-major axis and e the eccentricity.
Earth's perihelion
Earth reaches perihelion around 3–4 January at roughly 0.983 AU, even though Northern Hemisphere winter occurs at this time — a reminder that seasons are caused by axial tilt, not distance to the Sun.
